1. Field of the Invention
The present invention relates to an image data processor for generating a page raster that is image data in a rasterized format by each page based on page description data described in page description language for variable printing, and an image data processing program storage medium storing an image data processing program that causes an information processing apparatus to operate as the image data processor.
2. Description of the Related Art
For example, there have been variable printing in which a variable object that is an image object used only once on a particular page is combined with a reusable object that is an image object used repeatedly over plural pages. One application of the variable printing is, for example, an advertisement addressed to a different individual name but contents of which is almost the same, for example, formed by picture patterns.
As variable printing has large data volume due to its abundant variation in printing, how to decrease data amount, speed up processing and suppress the amount of data storage capacity raise a problem.
Here, it should be noted that there has been proposed a technique in which, when plate data for variable printing is generated from layout information that has already been generated in the previous processing using merging processing of an object data, the same plate data is reused without merging the relevant image (see Japanese Patent Laid-Open No. 2005-210483). For example, if a plate data C for the third page is found to be same as a plate data C for the first page that has already been generated, the first-page plate data C is to be sent to a printer as the third-page plate data C.
Generally, variable printing has a structure most of which is formed by adding a small number of variable objects to almost same page layouts. Recently, there has been increasing number of jobs in which one set is formed by plural pages. An example taken here is a pamphlet for merchandise classified by customers that has four pages as one set: the first page is formed by variable data representing customers; the second page to the fourth page are reusable pages selected according to customers' taste from twenty kinds of prepared pages introducing merchandise. Each variable job is formed by 999 sets for 999 customers.
A printing operator tends to print on a sheet as large as possible to suppress cost of paper and printing. For example, if the page size in the above example is A4 size, they impose two pages of A4 size on an A3 sized sheet and cut it into two in the subsequent processing.
In the case of a job described above, if, in A4-size printing, twenty kinds of reusable pages and one variable page out of four pages are generated, the already prepared print data (i.e., approx. 75% of the total) can be used for the remaining pages, which leads to high productivity. However, if two pages are imposed on a sheet, the number of combinations for arranging the right half and the left half of a sheet is as much as 400. This reduces the ratio in which the same objects are arranged in the same position of a sheet. Thus, a reuse ratio is decreased (to approx. 30% of the total).